Composite body, production process and use

ABSTRACT

Disclosed are a composite body and the production and the use thereof. It consists of a substrate body with a single- or multilayer coating, containing either Ti, Zr, Hf, V, Nb carbides, nitrides, carbonitrides and/or Ta and/or Al 2 O 3  or ZrO 2 . In order to improve the characteristics of wear from chip removal or another form of abrasion, the invention suggests that a layer of Zr, Hf, V, Nb, Ta or Cr carbonitride be precipitated either directly upon a layer of Al 2 O 3 — or ZrO 2 — or upon a thin intermediate layer of ZrC or ZrN up to 0,5 μm, or upon a TiN layer up to 0.1 μm, or indirectly upon a layer of Al 2 O 3 — or ZrO 2 —.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a national stage of PCT/DE/96/02519, filedDec. 30, 1996, based upon German national application 196 41 468.7 and296 17 507.2 of Oct. 9, 1996 under the International Convention.

1. Field of the Invention

The invention relates to a composite which is comprised of a substratebody with a coating of one or more layers of carbides, nitrides,carbonitrides of Ti, Zr, Hf, V, Nb and/or Ta and/or of Al₂O₃ or ZrO₂.

The invention also relates to a process for producing a coating from acarbonitride of the aforementioned metals by CVD or plasma activated CVDon a base body or on a coated base body of a hard metal, cermet, steelor a ceramic.

2. Background of the Invention

The first coatings of the type with which the invention is concern whichhave become known according to the state of the art, are comprised oftitanium carbide with a thickness of up to 8 μm with which an improvedwear resistance effect against free-surface wear can be obtained.Further there are double or multiple coatings of titanium carbide andtitanium nitride, especially with an outer layer of titanium nitride,which belong to the state of the art and with which a reduced corrosioncan be achieved with cutting inserts used for chip removal. For furtherimprovement of such cutting inserts, multilayer coatings with the layersequence TiC, Ti(C,N)—TiN have been proposed. In addition, it has beenfound that the natural brittleness of ceramics like Al₂O₃ can beminimized when Al₂O₃ in thin layer form is deposited thereon and alsoTin, Ti(C,N) and an outer layer of Al₂O₃ can comprise multilayercoatings for such use. While the patent literature, for example in theframework of a special coating process as in EP 0 229 282 B1, generallyspeaks of carbides, nitrides and/or carbonitrides of the elementstitanium, zirconium, hafnium, vanadium, niobium and/or tantalum, thedescribed examples are limited to titanium compounds as the coatingmaterial, in part, in combination with aluminum oxide. Correspondinglythe same can be said for ZrO₂ in combination with or as a replacementfor oxide-containing coatings. First in DE 36 20 901 A1 or EP 0 250 865A1 (with the same contents) a cutting insert is described whose edge iscoated with titanium carbide, titanium carbonitride and/or titaniumnitride and whose outer cover layer is comprised of a thin zirconiumnitride coating. The zirconium nitride which has poorer wearcharacteristics than the aforementioned titanium compounds, is intendedto hinder oxidation of the basic layers underlying this layer byatmospheric oxygen so the good wear characteristics of the titaniumcarbide-titanium carbonitride-and/or titanium nitride coatings are fullyretained. In practice, zirconium compounds are not normally used ascoating materials.

However, in U.S. Pat. 3,854,991 (or CH-A-585 273) a coated sintered hardmetal product is described in which the coating is comprised of HfCNand/or ZrCN and has X-ray diffraction lattice constants which in thecase of HfCN and a mixture of HfCN and ZrCN lie between 4.570 and 4.630angstrom and in the case of ZrCN lie between 4.6 and 4.62 angstrom. Inthe case of ZrCN, the C/N ratio is clearly less than 1. To produce thishafnium or zirconium carbonitride, a hafnium and/or zirconium halogenideis conducted together with hydrogen, nitrogen and a hydrocarbon at atemperature of 1000 to 1300° C. across a substrate.

OBJECT OF THE INVENTION

It is the object of the present invention to provide a substrate bodyhaving a multilayer coating whose wear characteristics for chip removalmachining or under otherwise abrasive loading is improved and has of anincreased life.

SUMMARY OF THE INVENTION

This object is achieved with composite body in which claim 1 which ischaracterized in that is composed of a carbonitride of Zr, Hf, V, Nb, Taor Cr and that this layer is deposited either directly upon an Al₂O₃ orZrO₂ layer or upon a thin intermediate layer of a maximum thickness of0.5 μm of TiN directly on an Al₂O₃ or ZrO₂ layer. The aforementionedcarbonitride layer preferably has a thickness of at least 2 μm to amaximum of 6 μm and/or the Al₂O₃ or ZrO₂ layer has a thickness of 2 μm,preferably 3 μm or more. The respective thicknesses are provided on thecutting corners of composite bodies which are formed as cutting inserts.It is also possible to form the outer layer of the aforementionedcarbonitride, especially ZrCN or HfCN, and also to apply one or moreouter layers on this carbonitride layer whereby the layer thickness orthe total thickness of the one or more outer layers does not exceed 2 μmand preferably does not exceed 1 μm. In other words in the framework ofthe present invention one can obtain equally good solutions when theaforementioned carbonitride layer has coated thereon even extremely thinfurther layers. Preferably when such composite bodies are used ascutting inserts for turning, the following layer thicknesses are used:TiN: 0.5 to 2 μm; TiCN: 9 to 13 μm; Al₂O₃: 2 to 4.5 μm and ZrCN: 2 to 4μm. For corresponding cutting inserts used for milling preferably thefollowing layer thicknesses are chosen: TiN: 0.5 to 2 μm; TiCN: 9 to 13μm; Al₂O₃ and ZrCN: 4 to 6 μm, whereby one of the layers Al₂O₃ and ZrCNis at least 1 μthick.

The substrate body can, according to a further feature of the inventionbe composed of hard metal, a steel, a cermet or a ceramic, especially amaterial based on Si₃N₄. Preferred hard metal substrate bodies arecomprised of 5.5 to 8.5 mass % Co, preferably 5.5 to 6.5 mass % Co as abinder, the balance WC. Alternatively, the substrate body can comprise 1to 3 mass % TiC, 2 to 5 mass % TaC, 1 to 3 mass % NbC and 5.5 to 8.5mass % Co, the balance WC.

For producing the carbonitride layer from Zr, Hf, V, Nb, Ta or Cr,according to a first alternative, a plasma-activated CVD is used inwhich the reactive gas atmosphere at the set reaction chamber, apartfrom hydrogen, argon and a chloride of the named metal, also containsionized and/or nonionized carbon-nitrogen donors with triple bonding,whereby the bond spacing between the carbon and nitrogen at roomtemperatures lies between 0.114 and 0.118 nm. Especially, the ionizedand nonionized C-N donors are generated by ionization and thermaldissociation of gasses of the cyanide group (CN-triple bonding) by meansof a plasma activation at temperatures between 400° C. and 700° C. and apressure of 100 to 1000 Pa. Suitable substances, which can liberatecyanide radicals (—CN) at the reaction temperature, are organiccompounds like hydrogencyanide, cyanamide, cyanogen, cyanoacetylene andacetonitrile. In the deposition, the substrate body can be connected asthe cathode for the plasma activation and a pulsed direct current can beapplied, such as the process described for example in DE 38 41 731 C1.

Alternatively it is also possible to apply the named hard materialcoating from carbonitride by means of CVD, whereby the gas phase, at areaction temperature between 700° C. and 1100° C. and preferably atpressures between 5 kPA and 100 kPa, contains, in addition to H₂ and/orAr and chlorides of the above-mentioned metals, also carbon donors andnitrogen donors which have a C—N molecular group. This is preferably acyanide group with a triple bond between the carbon and nitrogen, whosespacing at room temperature amounts to between 0.114 and 0.118 nm. Suchcompounds are hydrogen cyanide, cyanamide, cyanogen, cyanacetylene oracetonitrile. Alternatively or in part, such gaseous compounds can alsobe used which have CN molecular groups with a single bond between thecarbon and the nitrogen. Molecules with single CN bonds includemethylamine and ethylenediamine. The present invention includes withinits framework appropriate substances containing the cyanide group;compounds of this kind are in principle known in the state of the artand are for example described in DE 25 05 009 A1. Other gaseous mediacan be gated into the reaction vessel which are capable of forming cyanogroups at the reaction temperature.

Preferred uses of the composite bodies according to the invention are asabrasively stressed wear parts or in the chip removal machining field,here especially for turning or milling.

In a concrete example, a hard metal substrate body with 6 mass % Co,balance WC, is provided with the following layer sequence from insideoutwardly in the indicated thicknesses: 1 μm TiN, 10 μm TiCN, 4 μm Al₂O₃and 3 μm ZrCN. The outermost zirconium nitride layer is of full density,free from cracks and has a positive compressive intrinsic stress. TheC/N ratio was about 1.

Cutting inserts used for chip removal machining in the milling, boringor turning fields have useful lives which, depending upon the chipremoval machining conditions which can be 1.2 to 4 times greater thanthe lives of multilayer coated composite bodies which are known from thestate of the art and which have as the outermost layer the layersequence TiN, Al₂O₃ or ZrN.

The good wear resistance can be obtained also when, instead of the outerZrCN cover layer other thin layers, for example of TiN are applied.However these cannot have as many layers beneath the layer combinationAl₂O₃/ZrCN and cannot have thicknesses of layers beneath the Al₂O₃/ZrCNlayer sequence as in the present case. The improved system of thepresent invention provides greater wear resistance with layers having atotal layer thickness which can amount to up to 26 μm in contrast toearlier arrangements. The same applies also for the case in whichzirconium in the carbonitride layer is completely or partly replaced byhafnium, vanadium, niobium, tantalum or chromium.

The good resistance to wear properties can also be realized when betweenthe layer sequence Al₂O₃/ZrCN, a thin intermediate layer of TiN of amaximal thickness of 0.1 μm to TiN or a thin layer of a maximum of 0.5μm of ZrC or ZrN is provided.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become morereadily apparent from the following description, reference being made tothe accompanying drawing in which:

FIG. 1 is a perspective view of a cutting insert according to theinvention;

FIG. 2 is a section along the line A-B of FIG. 1 drawn to a largerscale; and

FIG. 3 is a view similar to FIG. 2 but illustrating another embodiment.

SPECIFIC DESCRIPTION

FIG. 1 shows a cutting insert 10, whose cutting corner 11 is shown insection along the line A-B in FIG. 2 or in an alternative configurationin FIG. 3, schematically.

As can be ascertained from FIG. 2, on a substrate body 12 which iscomprised of a WC hard metal with 6% Co as a binder, a first 1 μm thicklayer 13 of TiN, a second 10 μm thick layer 14 of TiCN, a further 4 μmthick layer 15 of Al₂O₃ and an outer 3 μm thick cover layer 16 of ZrCNare applied.

The embodiment of FIG. 3 differs from the aforementioned embodimentaccording to FIG. 2 in that between the layers 16 of ZrCN and the layer15 of Al₂O₃ there is provided a 0.1 μm thick layer 17 of TiN.Additionally an outer 0.1 μm thick TiN layer is provided as the outercoating layer.

From the subsequent chip removal machining results it can be seen(independently of the type of turning plate) that turning plates coatedaccording to the invention have significantly longer operating livesthan the turning plates known from the art.

EXAMPLE 1

Workpiece: Ball bearing ring, diameter 152×36

Material of workpiece: Steel 100Cr6

Cutting speed: 280 m/min

Feed: 0.8 mm/per revolution

Cutting depth: 1.0 mm

Turning plate State of the art According to the invention Plate shapeSNMG120416 SNMG120416 Coating Ti(C,N)—Al₂O₃—TiNTiN—Ti(C,N)—Al₂O₃—Zr(C,N) Layer thick-  15  15 ness total (μm)Workpieces 125 150 per cutting corner

EXAMPLE 2

Workpiece: Axle pin, diameter 40×100

Material of workpiece: Steel C55

Cutting speed: 200 m/min

Feed: 0.7 mm/per revolution

Cutting depth: 2.5 mm-3.0 mm

Turning plate State of the art According to the invention Plate shapeWNMG050414 WNMG050414 Coating TiC—Al₂O₃—TiN TiN—Ti(C,N)—Al₂O_(3—Zr(C,N))Layer thick-  15  15 ness total (μm) Workpieces 195 235 per cuttingcorner

EXAMPLE 3

Workpiece: Free-running ring

Material of workpiece: Steel Ck45

Cutting speed: 220 m/min

Feed: 0.25 mm/per revolution

Cutting depth: 2 mm

Turning plate State of the art According to the invention Plate shapeWNMG050408 WNMG050408 Coating TiC—Al₂O₃ TiN—Ti(C,N)—Al₂O₃—Zr(C,N) Layerthickness total 15  14 (μm) Workpieces per 50 143 cutting corner

EXAMPLE 4

Workpiece: Drive shaft 50 mm diameter×310

Material of workpiece: Steel 16MnCr5

Cutting speed: 260 m/min

Feed: 0.4 mm/per revolution

Cutting depth: 2 mm-3 mm

Turning plate State of the art According to the invention Plate shapeDNMG150612 DNMG150612 Coating TiC—Al₂O₃—TiN TiN—Ti(C,N)—Al₂O₃—Zr(C,N)Layer thickness  14  14 total (μm) Workpieces per 130 170 cutting corner

What is claimed is:
 1. A composite comprising a substrate body with amultilayer coating which includes at least: a) a first, 0.5 μm to 2 μmthick inner layer of TiN; b) a second, 9 μm to 13 μm thick layer of acarbonitride of an element of the group IVa of the periodic system; c) athird, at least 2 μm thick of Al₂O₃ or ZrO₂; and d) a fourth outer layerof a carbonitride of Zr, Hf, V, Nb, Ta or Cr with a thickness in therange of 2 μm to 6 μm .
 2. The composite according to claim 1 whereinsaid coating has a layer sequence of 0.5 μm to 2 μm thick TiN; 9 μm to13 μm thick TiCN, 2 μm to 4.5 μm thick Al₂O₃ and 2 μm to 4 μm thickZrCN.
 3. The composite according to claim 1 wherein between the thirdand the fourth layers an intermediate layer is provided which iscomprised of ZrC or ZrN with a maximum thickness of 0.5 μm or of TiNwith a maximum thickness of 0.1 μm.
 4. The composite according to claim1 wherein the third layer has a thickness of at least 3 μm.
 5. Thecomposite according to claim 1 wherein the outer layer of a carbonitrideof Zr, Hf, V, Nb, Ta or Cr, additionally one or more outer layers aredeposited, whereby the total thickness of the one or more layers doesnot exceed 2 μm .
 6. The composite according to claim 1 wherein thetotal thickness of the third and fourth layers is at least 5 μm to amaximum of 10 μm .
 7. The composite according to claim 1 wherein thesubstrate body is comprised of hard metal, steel, a cermet or a ceramic.8. The composite according to claim 7 wherein the substrate body is anSi₃N₄ ceramic.
 9. The composite according to claim 7 wherein thesubstrate body is comprised of 5.5 to 8.5 mass % Co, the balance WC. 10.The composite according to claim 9 wherein the hard metal is comprisedof 5.5 to 6.5 mass % Co as a binder, the balance WC.
 11. The compositeaccording to claim 7 wherein the substrate body is a hard metalcomprised of 5.5 to 8.5 mass % Co as a binder, 1 to 3 mass % TiC, 1 to 5mass % TaC, 1 to 3 mass % NbC, the balance WC.
 12. A method of making acomposite comprising the steps of: (a) forming a substrate body of ahard metal, steel, a cermet or a ceramic with a TiN coating; and (b)depositing a carbonitride of Zr, Hf, V, Nb, Ta or Cr on said TiN coatingby plasma activated CVD at a reaction temperature from a reactive gascontaining hydrogen, argon, a chloride of Zr, Hf, V, Nb, Ta or Cr, andan ionized or nonionized carbon-nitrogen donor with carbon-nitrogentriple bonding and a carbon-nitrogen bond distance of 0.114 to 0.118 nm.13. The method defined in claim 2 wherein the ionized or nonionizedcarbon-nitrogen donor is formed by ionization and thermal dissociationof a gas containing cyanide groups by plasma activation at a temperaturebetween 400° C. and 700° C. and a pressure of 100 to 1000 Pa.
 14. Themethod defined in claim 13 wherein the plasma activation is effectedwith pulsed direct current and the substrate body connected as acathode.
 15. A method of making a composite comprising the steps of: (a)forming a substrate body of a hard metal, steel, a cermet or a ceramicwith a TiN coating; and (b ) depositing a carbonitride of Zr, Hf, V, Nb,Ta or Cr on said TiN coating by plasma activated CVD at a reactiontemperature between 700° C. and 1100° C. and a pressure of 5 kPa to 100kPa from a reactive gas containing hydrogen, argon, a chloride of Zr,Hf, V, Nb, Ta or Cr, and an ionized or nonionized carbon-nitrogen donorwith a carbon-nitrogen molecular group.
 16. The method defined in claim15 wherein said carbon-nitrogen donor has a cyanide group withcarbon-nitrogen triple bonding and a carbon-nitrogen bond distance of0.114 to 0.118 nm.
 17. The method defined in claim 16 wherein saidcarbon-nitrogen donor is acetonitrile.
 18. The method defined in claim15 wherein said carbon-nitrogen molecular group has a single bondbetween the carbon and the nitrogen.